May be it's just a locational problem?

I have not seen any people with ping higher than 150 when I join EU games from UK.

You are probably being proxied. Are you in Europe or Australia?

There are a lot of reasons you could be experiencing higher than normal ping in one game over another.

Are you getting the same Ping to everyone or are there people who you connect to with much higher and much lower pings than normal?

Check your connection window - in the list of players you're connected to, do any of the player's names have (Proxy) after them?

Have you completed a Speed Test of your internet connection yet?

Does your Ping 'spike' up and down, or does it remain a constant number?

In order to benchmark your connection, we'll need more detailed information. Please go here and post back the information it gives.

Being there are no spikes in the ping it's doubtful there are background applications running chewing up your bandwidth - however as always make sure Demigod is the only program running. Close everything, including Impulse. The ping your seeing to everyone else is not their Ping, rather your Ping to them. As Demigod is a P2P game, everyone is connected to everyone else directly. There is no server, and thus people can have drastically different Pings to other players.
However, as your ping to everyone is higher than normal, this can mean that your connection is being throttled by your ISP. If there are more people in the game, is your ping higher? For example, if there are only 2 people in the game, is your Ping to each player acceptable?

Using the proxies is a good way to connect if your having connection issues - however at current there is no location logic; everyone, regardless of where they're from, connects to the same proxy. This means if you live far away from the proxy it's not going to help you until they've updated them.

I've made a post here. Run through the steps in that thread, and see what the results are.

The only thing I can think of DemiCom, is realted to your upload speed; Demigod requires more Upload Bandwidth than most games of a similar nature. Try running your game through the proxies only - I can't recall the exact command to achieve this however it's been listed in several of Frogboy's journals - and see if this effects your Ping further, or if it stays the same and post back here.